We were just scrambling out of the depths of the chasm when I happened to glance back and see him. Outlined in the emerald-lichened rock was the rugged profile of a knight's head with a jutting Desperate Dan jaw, beetle brows and a helmet.

The life-like rock formation resembled, I thought, one of the many legendary figures connected with the hiding place.

When I first visited Lud's Church, a deep crevice in Back Forest in the Staffordshire Moorlands, my head was full of Arthurian legend. I'd just read Sir Gawain and the Green Knight, the classic 15th-century poem, and the chasm has been identified by some as the Green Chapel mentioned in the tale. And Robin Hood, Friar Tuck and Bonny Prince Charlie have all been connected with the hiding place too.

Threatening clouds masked the sun when I visited, and mists wreathed the serrated pinnacles of Castle Cliff Rocks overlooking the valley of the Dane, as we walked up through the trees from the packhorse bridge across the river near Gradbach.

We had some trouble finding Lud's Church - marked on the map as a cave but actually a huge dog-legged landslip some 100 metres long and 15 metres deep.

Inside, everything was green. Dripping grasses, mosses and ferns clung tenaciously to the vertical sides of the ravine and weeping trees overhung the top.

The name of the cave may come from the Celtic god Llud, or more likely from Walter de Lud Auk, a 14th-century follower of John Wycliffe, an early church reformer who held illicit services here far from the prying eyes of the authorities. These followers were known as the Lollards.

One day a raid took place during one of these services and Walter's daughter, Alice, was accidently shot. She is still said to haunt the chasm, along with a headless figure echoing the beheading ritual of Gawain and the Green Knight.

• OS map ref: SJ 987656; nearest town: Gradbach

Dragons' dens: where to find mysterious caves

Smoo Cave, Scotland

It looks like classic dragon territory - a dramatic, night-black hole set into a limestone cliff face, with grassy pastures above. In its guts are an active river with a deep sink hole, underground waterfalls and huge chambers. Local scare stories say spirit guards, devils, smugglers and highwaymen once dwelled here, but the only evidence of human occupation is prehistoric. It's safe to explore, but you'll need a dinghy to access the watery third chamber.• Near Durnesssmoocave.org

White Scar, Yorkshire

Hidden beneath Ingleborough Hill in the Dales, a subterranean world of weird cave formations, streams, waterfalls and prehistoric mud pools and a huge ice age cavern hung with thousands of stalactites forms the UK's longest show cave.whitescarcave.co.uk

Sculptor's Cave, Scotland

Around 3,000 years ago, archaeologists believe people in the north of Scotland brought their dead children to this sea cave near Lossiemouth, Morayshire, which was used as a natural temple. Skull parts found near the cave's entrance suggest they erected their heads on poles as a rather gruesome memorial. It can only be accessed at low tide from the shingle beach.

Mendips, Somerset

Wookey Hole and Cheddar Gorge caves are famous and open to the public, but did you know experienced cavers can apply to gain entrance to secret passages beyond their show caves?wookey.co.uk, cheddarcaves.co.uk